In the process of treating waste water containing biodegradable materials, rotary biological contactors have been found to be useful for the purpose of promoting bacterial action. Such rotary biological contactors are usually rotary devices with plastic sheet material arranged to rotate through a tank of waste water and then be exposed to air in each revolution. A biomass, or biological slimes, are established on the surfaces of the plastic material, and as the rotary biological contactor revolves, it is desirable that the biomass on the plastic media be exposed to air in each cycle.
Such rotary biological contactors are large in size, typically 10 to 12 feet in diameter, and typically 15 to 25 feet more or less in length. As a result, the rotary biological contactors are expensive and are intended to have a long service life, typically in the range of 20 years or more. Numerous problems have been experienced with various materials used in such biological contactors, and of course, the shutdown and repair of such equipment adds significantly to the expense of operation.
The plastic media has taken numerous forms in the past. Oftentimes plastic disks or wafers, constructed of polystyrene, polyethylene or expanded styrofoam have been mounted on a rotating shaft with portions of the disks being immersed in the tank of waste water in each revolution. Such rotary biological contactors using disk type media are illustrated in a number of prior patents as follows:
______________________________________ 3,630,366 3,777,891 3,827,559 3,904,525 3,997,443 British 935,162 ______________________________________
A major problem with such disk-like media is the difficulty in mounting the disks to the rotary shaft to accomplish long service life. Such disk-like media have not proven to be highly satisfactory in industrial and municipal type installations.
Other plastic media have utilized cube shaped filter sections mounted on framework spaced from the rotation axis. Such sections have used plates extending along and confronting the rotation axis and grid-like media. These sectioned media are illustrated in U.S. Pat. No. 3,847,811 and British Pat. No. 1,397,664. Such media as illustrated in these patents, has severely limited service life and high maintenance costs.
Other rotary biological contactors have used cylindrical cages of wire screen containing many plastic balls defining the plastic media on which the biomass is established. These are typified by U.S. Pat. Nos. 3,956,127 and 4,200,532. Such rotary biological contactors, as is illustrated in these patents, have limited service life and high maintenance costs.
A rotary biological contactor with a wound spirally arranged plastic sheet material is illustrated in U.S. Pat. No. 4,115,268, and has proven to be extremely reliable with long service life. Occasionally, rupturing of welds between adjacent turns of the plastic sheet material have caused some problem in deterioration of the media, requiring maintenance.
The rotary biological contactors have been mounted in the tanks of waste water in various ways, typically on fixed bearings as illustrated in U.S. Pat. No. 4,200,532. In other instances, the plastic media, using floating plastic balls of the type illustrated in U.S. Pat. No. 4,200,532 has simply been allowed to float in the water, as illustrated in a trade brochure entitled Carter Bio-Drum and The Activated Bio-Film Method, published by Ralph B. Carter Company, 192 Atlantic St., Hackensack, N.J., 07602, prior to 1980; and in U.S. Pat. No. 3,956,127.
Such rotary biological contactors have been revolved in the waste water treatment by electric motors turning the mounting shaft or through the use of air bubbling through the water and into pockets of the rotary biological contactor, as illustrated in U.S. Pat. No. 3,886,074.
While various systems of rotary biological contactors have attempted to address the service life problem with minimal maintenance, none of the prior art has adequately solved this problem. Accordingly, breakdowns and shutdowns of equipment has been necessary, resulting in high maintenance costs, and discharge of inadequately treated waste waters into public drainage and river systems.